Oldest Evidence of Plate Tectonics Dates Back 3.5 Billion Years
Ancient rocks in Western Australia have yielded the oldest direct evidence yet that Earth’s tectonic plates were moving as early as 3.5 billion years ago, according to a study published March 19 in the journal Science. The findings challenge previous assumptions about the early Earth and suggest that plate tectonics, the process that shapes continents and drives volcanic activity, began much earlier than previously thought.
The research, led by Alec Brenner, a Ph.D. Candidate at Harvard University, and Professor Roger Fu, also of Harvard, focused on the Pilbara Craton, one of the oldest and most stable parts of the Earth’s crust. Analysis of over 900 rock samples collected from more than 100 locations within the North Pole Dome region of the Pilbara Craton revealed significant shifts in the region’s latitude and rotation over a period of roughly 30 million years, starting around 3.5 billion years ago.
“There has been a huge range of ages suggested for timing,” said Brenner, who is now a postdoctoral researcher at Yale University. “With this study, we’re able to say three and a half billion years ago, we can see plates moving around on the Earth surface.”
The team employed paleomagnetism, a technique that uses the magnetic properties of rocks to reconstruct their past positions. Tiny magnetic crystals within the rocks act as a record of Earth’s magnetic field at the time the rocks formed. By analyzing the alignment of these crystals, researchers can determine both the latitude and orientation of the rocks, effectively using them as an ancient GPS. The Pilbara Craton samples showed a drift of tens of centimeters annually and a clockwise rotation exceeding 90 degrees.
The study’s findings contrast with earlier research on rocks from the Barberton Greenstone Belt in South Africa, which indicated that region remained relatively stationary near the equator during the same period. This suggests that different parts of the Earth’s crust were moving independently of one another in the early Archean Eon.
“We took a really big gamble,” Brenner said. “Demagnetizing thousands of cores takes years. And boy, did it pay off! These results were beyond our wildest dreams.”
The research also identified the oldest known geomagnetic reversal – a flip in Earth’s magnetic field where the north and south magnetic poles switch places – dating back to the same period. This reversal is thought to be driven by the movement of molten iron within Earth’s core. Fu noted that the frequency of these reversals appeared to be lower 3.5 billion years ago than it is today, potentially indicating a different dynamic within the Earth’s core.
Scientists have long debated the timing of the onset of plate tectonics, with estimates ranging from 4 billion to 1 billion years ago. The novel findings support the idea that plate movement played a crucial role in stabilizing Earth’s environment and creating conditions conducive to the development of life. The Pilbara Craton also contains evidence of some of the earliest known life forms, including stromatolites and microbialite formations created by single-celled organisms.
“Almost everything unique about the Earth has something to do with plate tectonics at some level,” said Fu. “At some point, the Earth went from something not that special, just another planet in the solar system with similar materials, to something very special. A very strong suspicion is that plate tectonics started Earth down this divergent track.”
The study does not definitively determine the type of plate tectonic activity that was occurring 3.5 billion years ago – whether it resembled the modern system of subduction and continental drift, or a different, earlier form. Further research is planned to investigate the specific mechanisms driving plate movement during the Archean Eon.